Process and apparatus for making lower aliphatic acid anhydrides



Feb. 25, 1941. D. c. HULL PROCESS AND APPARATUS FOR MAKING LOWER ALIPHATIC' ACID ANHYDRIDES Filed Jan. 21, 1938 m L DE]! R A A p m mm H E T m M W M W 3 0 T A A M C V 2 u T 4 I 8 RM E. 6 m mm 7\ m T DE It m c A E T 4| H mm? M mfiS 9 2 P AE WELE 5 CN cTmfi HH/ 2 M WMAG .I f C I N w um RBT AL mmm Mm NT .5 D GM 1 g c I1 mm mm 1 mqm N X Dw R 3 .H M I O f A L 8 CE A H m U a ll R. WUWK U UHHU 5 PIN B CTI. .l E V m H D 6 {11' 1 2 E IRE L v 8 U 5 m 1 z im \& m z m WM 2 mm D nU 9. MET w m UM PYROLYSIS CHAMBER (CHROMIUM,ALUMINUM ALLOY STEEL) DAVID C. HULL INVENTUR A TTOZ. i5 Y5 Patented Feb. 25, 1941 v rnocass AND APPARATUS For: MAKING LowEn smrna'rrc ACID aNmznnmEs David Hull, Kingsport, Tenn., assignor to East- I man Kodak Company, Rochester, N. Y., a corporation of New Jersey Application January 2 1, 1938, Serial No. 186,151 7 Claims. (01. 260-547) This invention relates to the manufacture of ketene and more particularly to improved meth- I ods for the manufacture of ketene and reaction products thereof such as acetic anhydride.

5 Various methods for the manufacture of ketene are known. In general. these methods comprise pyrolyzing acetone. Some processes also concern pyrolyzin'g acetic acid or acetic anhydride to ke tene. In general, all the prior art processes either 10 definitely state or by setting forth examples, in-

dicate that the pyrolysis treatment should be carried out in carbon or copper pyrolysis apparatus. For example, U. S. 1,975,663 describes a process for the manufacture of ketene wherein 15 the preheating of the ketenizable material is carried out in chrome-steel apparatus but the pyrolysis step is specified as being carried out in a copper reaction chamber.

While copper is satisfactory because of its new 2 catalytic activity with respect to ketene, from the structural standpoint and for high temperature use, copper presents certain disadvantages.

For example, it maybecome necessary to sheath or otherwise protect the copper reaction chamber 25 in order to prolong its life.

The prior art also describes ketene processes in which various basic nitrogen-containing com- ,ponents areadded to the reaction materials at various points for catalytic or other effects. The

0 prior art also describes processes in which ketenecontaining reaction products are immediately contacted with a liquid that reacts with the ketene, for the purpose of the cooling thereof as well as the formation of ketene reaction products.

35 However, in view of the high temperature of the ketene, it is apparent that the amount of liquid reagent required to cool the ketene gases is excessively greater than the amount necessary to form the reaction product. Hence, the excess 40 added for cooling causes excessive dilutionof the reaction product.

It also has been proposed to separate the other components from the ketene, as by drastic cooling, and thenreacting the separated ketene with acetic acid or other chemical for producing the desired reaction product. While this latter type of process of reacting separated ketene, is satis tory and produces high quality reaction products 50 in large yields, such processes require a substantial amount of cooling brine. Hence, refrigeration costs may be quite substantial. Also, in view -of the low temperatures employed in some instances, existing refrigeration equipment may be 55 unsuitable; or in small installations it may be u-nfeasible to construct refrigeration equipment for the particular process.

After extended investigation of ketene processes I have found that, contrary to prior art teachings, ketene may be formed in ferrous metal reaction chambers not heretofore known to be satisfactory. Also, I have found that various other improvements may be carried out that render the production of ketene simpler, more efficient and less costly in certain respects, particularly in respect to refrigeration and heating. I This invention has for one object to provide an improved method for the manufacture of ketene and its reaction products from various ketenizable organic substances. Still another 010- ject is to provide a process for the manufacture of ketene which may be applied to various organic substances such as acetone, acetic anhydride, acetic acid and the like. Still another object is to provide a pyrolysis process for the manufacture of ketene wherein the pyrolysis step may be carried out in a reaction chamber containing a substantial content of ferrous metal. Still another object is to provide a process for the manufacture of ketene or its reaction prod- .25 ucts, that at least partly may be carried out under reduced pressure. Still another object is to provide a pyrolysis process for the manufacture of ketene wherein preheating, pyrolysis, and other related heating steps may be conducted at high temperatures, if desired. Still another object is to provide a process for the manufacture of ketene or its reaction products wherein the combination or other transformation of ketene may be deterred. Still another object is to '35 provide a. process particularly adapted for the preparation of acetic anhydride from ketene. A still further object is to provide a process for the manufacture of acetic anhydride wherein the complete cooling and separation of ketene is not 40 required. Still another object is to provide a process for the manufacture of acetic anhydride from ketene wherein the heat of reaction may be usefully employed in the process. Other objects will appear hereinafter.

In the description of certain parts of my inven tion reference will be made to the attached drawing forming a part of the present application. The drawing is a semi-diagrammatic side elevation view somewhat in the nature of a flow sheet, 60 showing one form of apparatus arrangement which might be employed in carrying out my invention.

My process may be carried out in any suitable apparatus set-up. That is, a ketenizable material such as acetic acid or acetone would be vaporized, preheated and then pyrolyzed. The vaporizer may consist of a simple coil, a metal still pot or the like. The preheater likewise may be of simple construction comprising merely an S-coil or the like. The pyrolysis chamber mayconsist of a single tube or coil or other type enclosed chamber. If desired, the chamber may be cylindrical and provided with a corebuster and more or less in accordance with' the apparatus shown in U. S. 1,677,363, so as to provide an annular chamber in which the pyrolysis may be carried out. Or, various other constructions might be employed. In regard to the cracking chamber, as already indicated. the prior art generally specifies copper and recommends against the use of iron and/or nickel-containing parts Copper, while satisfactory, has certain disadvantages and does not possess particularly long life at the high temperatures which I prefer to operate my process at in some instances.

In contrast thereto, I have found that the pyrolysis chambers in ketene processes may be constructed of chrome-aluminum or chromenitrogen steels. The first-mentioned steel is preferred, inasmuch as it will readily withstand temperatures of 1000 C. or higher.

I have found that apparatus for the pyrolysis of acetone or other material to form the corresponding ketene may be made of an alloy approximately of the following composition:

Per cent Cr 20.00-21.50 Al 2.00- 2.50 Si 1.00- 1.40 Mn 0.50 Maximum C 0.08 Maximum Ni 0.30 Maximum Balance-substantially iron This material has the advantage over copper in that it is not oxidized at operating temperatures and it has the advantage over silver in costs. Yields may be obtained that are as good as those obtained by using either copper or silver.

While the above composition is preferred, since it has been found particularly satisfactory, percentages between, say for example 840% chromium, .5-15% aluminum, .02-6% silicon, the bal-' ance substantially iron, represent alloys of a range of compositions which might be employed but which are not considered as satisfactory as the preferred composition described. Examples of other proportions which are satisfactory are 20%-30% chromium, small amounts of silicon, manganese. carbon, and between .5%-l5% of an element selected from the group consisting of aluminum and nitrogen, the balance of the steel comprising essentially iron. Or there may be employed between 2l%-30% chromium. small amounts of manganese'and carbon, and betwe n .5%-15% of an element selected from-the group consisting of aluminum and silicon, the balance of the steel comprising iron. In the event a chrome nitrogen steel were employed, the aluminum content may be reduced or omitted. The nitrogen content would range from for example, .2-5%. The other elements would be as already described.

While I do not wish to be bound by theory of operation, it may be that my ferrous alloy satisfactory functions because, for example, the aluminum forms a thin resistant skin on the surface of the alloy. The chrome-aluminum and chromenitrogen steel not only may be used in the construction of the pyrolysis chamber, but may also be employed in constructing various other parts, where condensation or wet acid vapors do not occur.

The set-up would include suitable means for introducing the catalyst. For example, provision may be made either before the preheater or the reaction chamber for the introduction of a volatile phosphorus-containing catalyst. Or, if desired, the reaction chamber might be in the form of a crucible adapted to contain the catalyst. Also, at some suitable point in the path of flow of the reaction materials may be provided a -means for introducing reagent for preventing the transformation of the ketene into other products, or reaction thereof with other materials present.

The pyrolysis chamber would be connected with a cooling device such as a condenser or the like. In my process this cooling device may be of relatively. small capacity as compared with comparable devices employed in the prior art. This is because in my process it is not necessary to drastically cool the reaction products, as will be more fully described hereinafter. The cooling device will be connected directly to a standard type of vacuum distillation column so that the reaction products after being cooled may be fed directly to the column. Intermediate these parts or at some other suitable point, such as adjacent to or in the column, may be provided a means for introducing acetic acid or other medium for reacting with the ketene.

For a better appreciation of an arrangement of apparatus such as described in the precedin paragraphs, reference is made to the attached drawing wherein 2 represents the exterior or furnace housing of the unit. Vaporirer means for the material to be treated is provided at 3. The vaporizer is connected by conduits 4 and I with the preheater 1. Somewhere along the lines 4 and B'provision is made for catalyst introduction as at The preheater is connected by conduit I to the pyrolysis chamber I I. In the particular arrangement shown, I have shown the coil or tube type of pyrolysis chamber referred to above. This chamber has already been described in detail and is comprised of the particular alloy steel of which several species of compositions have been set forth in preceding paragraphs. The pyrolysis chamber is connected by conduit I! to a cooling device II which may be of conventional construction. However, as indicated, a small unit functions satisfactorily in my apparatus. This is due to the fact that, as has been pointed out in my process, it is not necessary to as drastically cool the ketene as has heretofore been considered necessary.

At some convenient point in conduit I! a means for introducing material for neutralizing the catalyst, may be provided as at I. The cooling device is connected directly into the vacuum column I5 which may be of any conventional construction. Hence, a detailed description is unnecessary. However, in my apparatus I provide conduit means I1 and I! through which the material. such as acetic acid, to be reacted with the ketene may be directly introduced. adjacent to or directly in the distillation column operating under reduced pressure.

The distillation column is provided with drawoff means I! at the base of the column. The upper portion of the column is provided with a vapor off-take conduit 2| which passes through the several condensers 22 and 23. The vacuum producwill react with the catalyst. In the ample where I have described the use of an ester ing means is connected to the apparatus at 24 through the vacuum receiver 26. The receiver discharges through conduit 21 to the trap 28 from which the contents may be removed through conduit 29.

It is to be understood that, of course, suitable means will be provided for supplying heat to the apparatus as at points 3 l-32 and the like; hence, a further description of such details appears to be unnecessary.

My invention may be further understood by consideration of the following more detailed description. This description is set forth for illusratin my Preferred embodiment hence, it is to be understood that the specific values and materials described are not to be construed as limiting my invention.

Anhydrous (glacial) acetic acid was fed to a vaporizer. This acid was preheated to several hundred degrees C. Subsequent to the preheating a small amount, namely, a fraction of a percent of a volatile phosphorus-containing catalyst was fed into the preheated stream. An ester such as triethyl phosphate is preferred as a catalyst but various other catalysts such as other esters of phosphoric acid, borates, or the like.

The preheated acetic acid was then conducted through the pyrolysis chamber which in .the instance of this example comprised a tube constructed of chrome-aluminum steel of the composition already described. The temperature in the pyrolysis chamber was maintained between 700 and 900 C. My novel reaction apparatus readily withstands such temperatures and if desired higher temperatures may be employed. The reaction chamber was maintained under reduced pressure. If desired, the .preheating and other steps in the process may also be carried out under reduced pressure. However, I contemplate preheating under atmospheric or other pressures.

In the example under description, the reaction mixture contained a substantial amount of ketene, a small amount of acetic anhydride, unreacted acetic acid, water, and various decomposition products such as carbon monoxide and the like. The reaction mixture was subjected to a cooling treatment. In connection with this step, it is desired to point out in some detail that this cooling treatment is not as drastic as heretofore considered desirable in the prior art. That is, the cooling, while rapid, is insuficient to cause any material separation of the components in the reaction mixture. A slight cooling retards to some extent the reaction of ketene with various other components. While in my process the ketene losses by reaction may be somewhat higher; than in certain other processes, nevertheless, I

have found that the refrigeration savings which I am able to make compensate to a large extent for any such losses.

In order to further reduce ketene losses during my process, the cooling step may be carried out in the presence of an excess of a reagent that present ex- 01 phosphoric'acid, I would prefer to carry out my cooling step in the presence of an excess of ammonia added to the reaction stream at any convenient point. It appears that catalysts for the decomposition of organic compounds into ketene are also frequently catalysts for the reaction of theketene with various other components of the reaction mixture. By my process 01 addmay be employed,

ing an excess of a reagent which reacts with the catalyst, the catalyst is either removed from the reaction mixture or by virtue of its reaction with the reagent reduced to a relatively inactive material. In the present example, the addition of an excess of ammonia as I have described, reacts with any of the phosphorus-containing catalyst after the ketene has been formed.

The cooled reaction mixture containing ketene, unreacted acetic acid, water and the various other components is treated without separating the ketene, with an amount of acetic acid approximately sufiicient to react with the ketene. The aforedescribed cooling step is carried out so that it, together with the cooling effect of adding a cool anhydrous acetic acid, reduces the temperature of the materials below 200 C. and generally substantially under 100 0. As already discussed, if all the cooling were supplied by cold acetic acid or other liquid, this would require a substantially greater quantity than that neces sary to react with the ketene, Hence, the result would-be that the excess would dilute theresultant acetic anhydride.

By my process, enough acetic acid is added to react with the ketene, the remainder of the cooling being supplied by other means, no disadvantages in the aforementioned respect are incurred. Furthermore, since in my process the amount .of cooling is insuflicient to produce material separation, less refrigeration is required. This consequently incurs since only approximately capacity than might be required for a moredrastic cooling.

Therefore, in my process after cracking a ketenizable material to ketene the reaction mixture would go through coolers. Suflicient acetic acid would be added for the ketene to react with the acid to form anhydride and for removing water formed. This mixture would then be fed directly intoa vacuum still, waste gas and all. Inthe vacuum still the ketene reaction occurs and the Water may be removed as a 80% acid from the top of the still. Strong anhydride, for example 50-80% may be removed from the bottom of the still or distilled off through a small column attached to the bottom. By my process I have found that the main portion of the heat for these distillations will be supplied by the reaction. It will be observed that since the stills are under reduced pressure, as for example between 10 and 250 mm. pressure, the boiling points of the various materials are correspondingly-reduced.

It will be observed that in my novel process both the cracking and the ketene reaction are carried out under reduced pressure. It will be further observed that my process diifers from certain prior art processes which have been briefly referred to in that any water in the reaction mixture would be separated after anhydride formation by reacting the ketene with acid, rather than separating the ketene before the anhydride formation. My process also difiers in certain other respects.

While from the standpoint of percentage yield and amount of ketene lost, it would appear that the above described process is not as emcient as certain prior art processes. Nevertheless, from the economic standpoint my process presents a number of advantages. As already indicated, my process oifers considerable savings, in refrigeration and heating requirements over the prior art processes. This permits the use of simpler and less expensive equipment as well as the more ready adaptation of existing equipment.

My process is susceptible of certain modifications. While I have described the pyrolysis of glacial acetic acid, it is also possible to pyrolyze dilute acetic acid. I have also found that both anhydrous and dilute acetone may be pyrolyzed in chrome-aluminum and chrome-nitrogen steel apparatus as described herein.

From the it -is therefore apparent that my process is susceptible of some modification, hence, I do not wish to be restricted in my invention excepting insofar as is necessitated by the prior art and the spirit of the appended claims.

What I claim is: l. A process for the manufacture of acetic anhydride, which comprises forming a reaction mixture containing ketene, unconverted feed and waste products, cooling the mixture under reduced pressure and to an extent insumcient to cause substantial ketene separation, mixing sufflcient cold glacial acetic acid to react, .under reduced pressure between and 250 mm., with the ketene but not in substantial excess of this amount, and immediately subjecting the mixture to a distillation treatment while still under reduced pressure wherein a substantial part of the heat is furnished by the heat of reaction of the ketene with acetic acid'and water is removed as a 'l0%-80% acetic acid.

2. A process for the manufacture of acetic anhydride, which comprises forming a reaction mixture containing ketene, unconverted acetic acid and waste products, cooling the mixture under reduced pressure and to an extent insuihlcient to cause substantial ketene separation, mixing therewith suflicient anhydrous acetic acid to react, under reduced pressure of between 10 and 250 mm., with the ketene but not substantially in excess of this quantity, then subjecting the mixture to distillation treatment while still under reduced pressure and at a temperature below C., wherein a substantial part of the distillation heat is furnished by the heat of reaction of the ketene with the acetic acid.

3. A process for the manufacture of reaction products of ketene, which comprises forming a reaction mixture containing ketene, unconverted feed, an ester of phosphoric acid as a catalyst and waste products, cooling the mixture under reduced pressure, and in the presence of excess ammonia to react with said catalyst, to an extent insumcient to cause substantial ketene separaketene with the acid.

4. A process for the manufacture of reaction products of acetic 'anhydride, which comprises forming a reaction mixture containing ketene, unconverted feed and waste products, cooling the mixture under reduced pressure and to an extent insufllcient to cause substantial ketene separation, incorporating with the reaction mixture sumcient lower aliphatic acid exothermically reactive toward the ketene to react therewith under reduced pressure between 10 and 250 mm., and immediately subjecting the mixture to distillation treatment at a temperature between 20' C. and 100 C., and at a pressure hetween 10 and 250 mm., wherein a substantial part of the heat is furnished by the heat of reaction of the ketene with the acid.

5. An: apparatus for thermally decomposing lretenizable organic substances to obtain products including ketene which comprises preheating means in series with a pyrolysing chamber, said chamber being constructed essentially of a steel having the composition 20-21.5% chromium. small amounts of manganese and carbon, and 24.5% of aluminum, the balance of the composition being essentially comprised pf iron, means for supplying said organic substances to the apparatus, and a cooling device for the product, connected to said chamber.

6. An apparatus for thermally decomposing ketenizable organic substances to obtain products including ketene which comprises preheating means in series with a pyrolyzing chamber, said chamber being constructed of a tube consisting of a steel having the composition 20-30% chr0- mium, small amounts of manganese and carbon, and .5% of aluminum, the balance of the composition'being essentially comprised of iron, means for supplying said organic substances to the apparatus, and a cooling device for the product, connected to said chamber.

'1. In an apparatus for thermally decomposing organic substances to obtain ketene comprising means for feeding the organic substances to the apparatus, preheater for the organic substances, a. pyrolyzing chamber essentially comprising a tube of a steel containing between 21%-30% chromium, small amounts of manganese and carbon, .5%-l5% of aluminum, the balance of the steel being substantially iron.

DAVID C. HULL. 

